1. Field of the Invention
The present invention relates to a process for the preparation of 2-(10,11-dihydro-10-oxodibenzo[b,f]thiepin-2-yl)propionic acid which is of value as a pharmaceutically acitive compound.
2. Description of prior art
It is known that 2-(10,11-dihydro-10-oxodibenzo[b,f]thiepin-2-yl)propionic acid having the following formula (I): ##STR2## (hereinafter refers to as dibenzothiepin derivative) shows a high anti-inflammatory action as well as a high analgetic action. The dibenzothiepin derivative is further known as a practically valuable anti-inflammatory agent with littel side effect. For example, the dibenzothiepin derivative and its pharmacological actions are described in Japanese Patent Provisional Publication No. 55(1980)-53282.
The above-mentioned Patent Provisional Publication discloses a process for the preparation of the dibenzothiepin derivative wherein 3-(.alpha.-cyanoethyl)-6-phenylthiophenylacetic acid is cyclized to give a dibenzothiepinpropionamide derivative and this derivative is then hydrolyzed.
Another process for preparing the dibenzothiepin derivative is disclosed in Japanese Patent Provisional Publication No. 57(1982)-106678. This process comprises hydrolysis of a phenylacetate ester having a nitrile group to give a dicarboxylic acid derivative and subsequent ring closure of the dicarboxylic acid derivative in the presence of a condensing agent such as sulfuric acid or polyphosphoric acid.
Another process for preparing the dicarboxylic acid derivative is disclosed in Japanese Patent Provisional Publication No. 58(1983)-113168 which comprises a propiophenone derivative is once converted into a hydroxyacetal compound. This process can be illustrated by the following equation: ##STR3## wherein Y is chlorine or bromine, R is an alkyl group having 1-5 carbon atoms or hydrogen, R' is an alkyl group having 1-5 carbon atoms, and R" is methyl or p-tolyl.
While the these known processes are employable for the preparation of the dibenzothiepin derivative, these processes have drawbacks in that the processes involve complicated and multiple steps or the use of a toxic reagent such as KCN. Accordingly, these known processes are not favorable as industrially employable processes.